Field of the Invention
The present invention is directed to a method of manufacturing printed wiring boards which control the drive of motors incorporated in a floppy disk drive, a compact disk drive, a VTR apparatus or the like.
Description of the Related Arts
Motors for rotating storage media such as floppy disks receive signals from printed wiring boards for motors, to control the drive thereof. FIG. 3 shows a coil circuit 30 of the printed wiring board. The coil circuit 30 comprises a substrate 31, a cancel loop circuit 32 and frequency generat FG circuit 33 provided on the substrate 31 in a parallel manner. The cancel loop circuit 32 is arcuate, while the (FG) circuit extends to form a continuous alternating rectangular corrugation around the cancel loop circuit 32. Circuit ends located at one side of the cancel loop circuit 32 and the FG circuit 33 are respectively connected with lands 34 and 35 formed on the substrate 31, while circuit ends located at the other side are electronically connected with each other by way of a connection wire 36. Such coil circuit 30 must to be subjected to electrical tests for open circuiting disconnection and short circuiting. To perform the electrical tests check-pins (not shown) of a tester or the like are brought into contact with the lands 34 and 35 for the application of voltage.
When the coil circuit 30 is electrically tested, a disconnection (open circuit) is easy to detect, but a short circuit is difficult to detect. This arises from the fact that even though there may exist a short circuit region designated as reference numeral 40 in FIG. 3, electrical continuity exist of the short circuit region 40 as if there were no electrical short, since the cancel loop circuit 32 ad the FG circuit 33 are electrically connected through the connection wire 36. This short circuit unconspicuously damages the function of the coil circuit 30, and therefore the defect is not detected until the printed wiring board has been loaded into the equipment of which it is a part.